This example uses the makeConstrainToRectFcn function to create a function that limits the area in which you can create or move an ROI to the size of the underlying image. By default, you can move an ROI off the image area.

imshow('cell.tif')
h = impoint(gca,20,60);
% Make a function that constrains movement of the point
x = get(gca,'XLim');
y = get(gca,'YLim');
fcn = makeConstrainToRectFcn('impoint',x,y);;
% Apply the constraint function to the ROI.
setPositionConstraintFcn(h,fcn);

Here is equivalent code, replacing use of makeConstrainToRectFcn function with the DrawingArea property of the ROI. By default, the new ROIs limit their creation and movement to the size of the underlying image, so there is no need to recreate that part of the example. Instead, this example creates a 10-pixel margin inside the image boundary where the ROI cannot go.

I = imread('cell.tif');
imshow(I)
h = drawpoint(gca,'Position',[20 60])
[height width] = size(I); %Get image dimensions
h.DrawingArea = [10,10,(width-20),(height-20)];